[PATCH 1/3] iio: adc: vf610: use ADC clock within specification
Jonathan Cameron
jic23 at kernel.org
Tue Jan 27 12:59:29 PST 2015
On 20/01/15 16:02, Stefan Agner wrote:
> Depending on conversion mode used, the ADC clock (ADCK) needs
> to be below a maximum frequency. According to Vybrid's data
> sheet this is 20MHz for the low power conversion mode.
>
> The ADC clock is depending on input clock, which is the bus
> clock by default. Vybrid SoC are typically clocked at at 400MHz
> or 500MHz, which leads to 66MHz or 83MHz bus clock respectively.
> Hence, a divider of 8 is required to stay below the specified
> maximum clock of 20MHz.
I hate to point out the obvious, by 83/8 > 20. Missing something?
>
> Due to the different bus clock speeds, the resulting sampling
> frequency is not static. Hence use the ADC clock and calculate
> the actual available sampling frequency dynamically.
>
> This fixes bogous values observed on some 500MHz clocked Vybrid
> SoC. The resulting value usually showed Bit 9 being stuck at 1,
> or 0, which lead to a value of +/-512.
>
> Signed-off-by: Stefan Agner <stefan at agner.ch>
In principle this looks fine to me. I would however like an
Ack from Fugang as the original author of the driver).
Given timing I probably wouldn't send this upstream until after
the merge window now (as it's stable material this won't really
matter).
Jonathan
> ---
> drivers/iio/adc/vf610_adc.c | 91 ++++++++++++++++++++++++++++++---------------
> 1 file changed, 61 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c
> index 8ec353c..e63b8e7 100644
> --- a/drivers/iio/adc/vf610_adc.c
> +++ b/drivers/iio/adc/vf610_adc.c
> @@ -141,9 +141,13 @@ struct vf610_adc {
> struct regulator *vref;
> struct vf610_adc_feature adc_feature;
>
> + u32 sample_freq_avail[5];
> +
> struct completion completion;
> };
>
> +static const u32 vf610_hw_avgs[] = { 1, 4, 8, 16, 32 };
> +
> #define VF610_ADC_CHAN(_idx, _chan_type) { \
> .type = (_chan_type), \
> .indexed = 1, \
> @@ -180,35 +184,47 @@ static const struct iio_chan_spec vf610_adc_iio_channels[] = {
> /* sentinel */
> };
>
> -/*
> - * ADC sample frequency, unit is ADCK cycles.
> - * ADC clk source is ipg clock, which is the same as bus clock.
> - *
> - * ADC conversion time = SFCAdder + AverageNum x (BCT + LSTAdder)
> - * SFCAdder: fixed to 6 ADCK cycles
> - * AverageNum: 1, 4, 8, 16, 32 samples for hardware average.
> - * BCT (Base Conversion Time): fixed to 25 ADCK cycles for 12 bit mode
> - * LSTAdder(Long Sample Time): fixed to 3 ADCK cycles
> - *
> - * By default, enable 12 bit resolution mode, clock source
> - * set to ipg clock, So get below frequency group:
> - */
> -static const u32 vf610_sample_freq_avail[5] =
> -{1941176, 559332, 286957, 145374, 73171};
> +static inline void vf610_adc_calculate_rates(struct vf610_adc *info)
> +{
> + unsigned long adck_rate, ipg_rate = clk_get_rate(info->clk);
> + int i;
> +
> + /*
> + * Calculate ADC sample frequencies
> + * Sample time unit is ADCK cycles. ADCK clk source is ipg clock,
> + * which is the same as bus clock.
> + *
> + * ADC conversion time = SFCAdder + AverageNum x (BCT + LSTAdder)
> + * SFCAdder: fixed to 6 ADCK cycles
> + * AverageNum: 1, 4, 8, 16, 32 samples for hardware average.
> + * BCT (Base Conversion Time): fixed to 25 ADCK cycles for 12 bit mode
> + * LSTAdder(Long Sample Time): fixed to 3 ADCK cycles
> + */
> + adck_rate = ipg_rate / info->adc_feature.clk_div;
> + for (i = 0; i < ARRAY_SIZE(vf610_hw_avgs); i++)
> + info->sample_freq_avail[i] =
> + adck_rate / (6 + vf610_hw_avgs[i] * (25 + 3));
> +}
>
> static inline void vf610_adc_cfg_init(struct vf610_adc *info)
> {
> + struct vf610_adc_feature *adc_feature = &info->adc_feature;
> +
> /* set default Configuration for ADC controller */
> - info->adc_feature.clk_sel = VF610_ADCIOC_BUSCLK_SET;
> - info->adc_feature.vol_ref = VF610_ADCIOC_VR_VREF_SET;
> + adc_feature->clk_sel = VF610_ADCIOC_BUSCLK_SET;
> + adc_feature->vol_ref = VF610_ADCIOC_VR_VREF_SET;
> +
> + adc_feature->calibration = true;
> + adc_feature->ovwren = true;
> +
> + adc_feature->res_mode = 12;
> + adc_feature->sample_rate = 1;
> + adc_feature->lpm = true;
>
> - info->adc_feature.calibration = true;
> - info->adc_feature.ovwren = true;
> + /* Use a save ADCK which is below 20MHz on all devices */
> + adc_feature->clk_div = 8;
>
> - info->adc_feature.clk_div = 1;
> - info->adc_feature.res_mode = 12;
> - info->adc_feature.sample_rate = 1;
> - info->adc_feature.lpm = true;
> + vf610_adc_calculate_rates(info);
> }
>
> static void vf610_adc_cfg_post_set(struct vf610_adc *info)
> @@ -290,12 +306,10 @@ static void vf610_adc_cfg_set(struct vf610_adc *info)
>
> cfg_data = readl(info->regs + VF610_REG_ADC_CFG);
>
> - /* low power configuration */
> cfg_data &= ~VF610_ADC_ADLPC_EN;
> if (adc_feature->lpm)
> cfg_data |= VF610_ADC_ADLPC_EN;
>
> - /* disable high speed */
> cfg_data &= ~VF610_ADC_ADHSC_EN;
>
> writel(cfg_data, info->regs + VF610_REG_ADC_CFG);
> @@ -435,10 +449,27 @@ static irqreturn_t vf610_adc_isr(int irq, void *dev_id)
> return IRQ_HANDLED;
> }
>
> -static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("1941176, 559332, 286957, 145374, 73171");
> +static ssize_t vf610_show_samp_freq_avail(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct vf610_adc *info = iio_priv(dev_to_iio_dev(dev));
> + size_t len = 0;
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(info->sample_freq_avail); i++)
> + len += scnprintf(buf + len, PAGE_SIZE - len,
> + "%u ", info->sample_freq_avail[i]);
> +
> + /* replace trailing space by newline */
> + buf[len - 1] = '\n';
> +
> + return len;
> +}
> +
> +static IIO_DEV_ATTR_SAMP_FREQ_AVAIL(vf610_show_samp_freq_avail);
>
> static struct attribute *vf610_attributes[] = {
> - &iio_const_attr_sampling_frequency_available.dev_attr.attr,
> + &iio_dev_attr_sampling_frequency_available.dev_attr.attr,
> NULL
> };
>
> @@ -502,7 +533,7 @@ static int vf610_read_raw(struct iio_dev *indio_dev,
> return IIO_VAL_FRACTIONAL_LOG2;
>
> case IIO_CHAN_INFO_SAMP_FREQ:
> - *val = vf610_sample_freq_avail[info->adc_feature.sample_rate];
> + *val = info->sample_freq_avail[info->adc_feature.sample_rate];
> *val2 = 0;
> return IIO_VAL_INT;
>
> @@ -525,9 +556,9 @@ static int vf610_write_raw(struct iio_dev *indio_dev,
> switch (mask) {
> case IIO_CHAN_INFO_SAMP_FREQ:
> for (i = 0;
> - i < ARRAY_SIZE(vf610_sample_freq_avail);
> + i < ARRAY_SIZE(info->sample_freq_avail);
> i++)
> - if (val == vf610_sample_freq_avail[i]) {
> + if (val == info->sample_freq_avail[i]) {
> info->adc_feature.sample_rate = i;
> vf610_adc_sample_set(info);
> return 0;
>
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